Apparatus for purification of exhaust gas and method for purification of exhaust gas using the same

Abstract

An apparatus for purification of exhaust gas comprises: an exhaust gas pipe (2) connected to an internal combustion engine (1); an upstream catalyst (3) arranged at the upstream side of an exhaust gas passage inside the exhaust gas pipe (2); a downstream catalyst (4) which is arranged at the downstream side of the exhaust gas passage inside the exhaust gas pipe (2), and on which nickel and / or iron is supported; and oxidizing gas supply means (5) which is connected to the exhaust gas pipe (2) between the upstream catalyst (3) and the downstream catalyst (4), and which supplies oxidizing gas into the exhaust gas pipe (2).

Description

TECHNICAL FIELD[0001]The present invention relates to an apparatus for purification of exhaust gas and a method for purification of exhaust gas using the apparatus.BACKGROUND OF THE INVENTION[0002]Catalysts for purifying exhaust gas from a gasoline engine, such as so-called NOx storage catalysts and three-way catalysts, have been put into practical use.[0003]Among these catalysts, NOx storage catalysts generally have a function to store NOx included in exhaust gas from an internal combustion engine when the air-fuel ratio of the exhaust gas is a lean state, and to release the stored NOx for reduction when the air-fuel ratio of the exhaust gas from the internal combustion engine is a theoretical (stoichiometric) or rich state. Such catalysts also have the nature of storing sulfur (S) components, in addition to NOx, included in the exhaust gas in a form of sulfate. Being highly stable compared to NOx, and impossible to be released from a catalyst simply by shifting an air-fuel ratio o...

AI Technical Summary

Benefits of technology

[0010]The present invention has been made in consideration of the above-described problems involved in the conventional techniques, an object of the present invention is to provide an apparatus for purification of exhaust gas in which the air-fuel ratio of exhaust gas flowing into a downstream catalyst can be rapidly shifted to a stoichiometric or lean state in accordance with changes in the operation condition of an internal combustion engine, in which the generation of H2S can be reliably restrained, and further in which functional decline of an upstream catalyst at the starting of the internal combustion engine can be avoided because the upstream catalyst is sufficiently protected from sulfur poisoning and thermal deterioration under a high-temperature lean state. Another object of the present invention is to provide an method for purification of exhaust gas using the apparatus.

[0011]The present inventors have devoted themselves to keen studies for achieving the above object, and, as a result, they found the fact that it is possible to be able to rapidly shift the air-fuel ratio of the exhaust gas flowing into the downstream catalyst to a lean state in accordance with the change in the operation condition of an internal combustion engine, that it is possible to be able to reliably restrain the generation of H2S, and that it is possible to prevent functional decline of the upstream catalyst at the starting by sufficiently protecting the upstream catalyst from sulfur poisoning and thermal deterioration under a high-temperature lean state, by using the following apparatus for purification of exhaust gas. The apparatus for purification of exhaust gas comprises: an exhaust gas pipe connected to an internal combustion engine; an upstream catalyst arranged at the upstream side of an exhaust gas passage inside the exhaust gas pipe; a downstream catalyst which is arranged at the downstream side of the exhaust gas passage inside the exhaust gas pipe, and on which nickel and / or iron is supported; and oxidizing gas supply means which is connected to the exhaust gas pipe between the upstream catalyst and the downstream catalyst, and which supplies oxidizing gas into the exhaust gas pipe. This discovery has led the inventors to complete the present invention.

Problems solved by technology

Therefore, such a catalyst may have caused a problem that NOx storage capacity is decreased due to the accumulation of sulfur components (such a phenomenon has been referred to as “sulfur poisoning (S poisoning)”).

Therefore, a large amount of SOx is emitted in a regeneration process of the catalyst.

However, the apparatuses for purification of exhaust gas described in Documents 1 to 5 are not capable of rapidly shifting the air-fuel ratio of the exhaust gas flowing into the catalyst at the downstream side to a lean state.

Accordingly, such apparatuses are unable to respond to a rapid change in the operation condition of an internal combustion engine, causing highly-concentrated H2S to be temporarily emitted in some cases.

Thus, when the atmosphere of the exhaust gas is shifted to a lean state, noble metal grains are caused to grow under the high-temperature lean atmosphere, and thereby the catalytic function is deteriorated.

For these reasons, with the upstream catalysts failing to fully function at the starting, the apparatuses for purification of exhaust gas described in Documents 1 to 5 do not sufficiently purify the exhaust gas in some cases.

In addition, in some case where a NOx storage catalyst or a generally-called three-way catalyst is used in the place of the catalyst at the downstream side, for example, when a high-load operation is brought to a stop, sulfur components accumulated on the downstream catalyst are temporarily desorbed in a form of highly-concentrated H2S, and thereby an exhaust odor is generated.

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